• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.4
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• pp.38-44
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• 2012

This paper presents experimental studies aiming at evaluation of structural behaviors of RC (Reinforced Concrete) beams externally strengthened with taper ended CFRPs(Carbon Fiber Reinforced Polymers). Experiments are performed with RC beams having different numbers of CFRP layers and length of each layer. The beams are subjected to four point-bending with simply supported condition. Test results of taper ended CFRPs and non-tapered CFRPs are compared and the better strengthening effect is observed from tapered ended CFRPs.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.596-596
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• 2013

본 연구에서는 Carbon nanotube 용액을 brush-painting 시스템을 이용하여 유연성 있는 PET 기판 위에 고품위의 플렉시블 투명전극을 제작하였다. CNT 박막의 두께에 따른 특성을 알아보기 위해 brushing 횟수를 증가시켜 UV/Vis Spectrometry, four-point probe 및 Hall measurement를 이용하여 전기적, 광학적특성을 알아보았다. 최적조건인 bilayer의 CNT 박막은 244 Ohm/sq.의 면 저항과 550 nm에서 68％의 투과도를 얻을 수 있었다. CNT 박막의 기계적 응력에 따른 전기적 안정성을 알아보기 위해 bending test를 진행하였다. 10,000번 구부려도 저항의 변화가 거의 없어 이 박막이 플렉시블한 소자에 적합하다는 것을 알았다. 유기태양전지의 적용 가능성을 알아보기 위해 CNT 박막을 유기태양전지의 anode 층으로 적용하여 1.6％ (VOC: 0.566(V), $J_{SC}$: 7.118(mA/$cm^2$), Fill Factor: 40.49(％))의 효율을 얻어 유기태양전지 소자의 적용 가능성을 알았다. 최종적으로 실험에서 성막된 CNT 박막은 기존의 CVD공정과 같은 복잡한 공정 대신에 쉽고 간편하게 고품위의 flexible brush-painting Carbon nanotube (CNT) 투명전극을 제작 하여 플렉시블한 유기태양전지 소자의 가능성을 알아보았다.

• Journal of Korean Association for Spatial Structures
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• v.17 no.4
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• pp.43-50
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• 2017

A type of one-way concrete composite slabs made by strain hardening cementitious composites (SHCC) deck combined with high tensile reinforcements was developed and evaluated by four-point slab bending test. The SHCC material was considered to have an high-ductile and strain hardening behavior in tension after cracking. From experimental comparisons with conventional reinforced concrete slab, the proposed SHCC and high tensile reinforced concrete composite slab showed more improved responses both in service and ultimate load capacities as well as in control of crack width and deflection.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.223-223
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• 2010

본 연구에서는 Al-doped ZnO (AZO) 박막을 linear facing target sputter (LFTS) 시스템을 이용하여 성막 하였고 박막의 특성을 분석하였다. LFTS 시스템은 마주보는 두 AZO 타겟 사이에 고밀도의 플라즈마를 구속시켜 플라즈마 데미지 없이 산화물 박막을 성막 시킬 수 있는 장치이다. LFTS로 성막된 AZO 박막의 인가된 DC 파워에 따른 전기적 특성을 분석하기 위해 four-point probe와 Hall measurement 장비를 이용하여 분석을 진행 하였으며, 광학적 특성 분석을 위해 UV/Vis spectrometer 장비를 이용하여 분석하였다. AZO 박막의 구조적, 표면적 특성을 분석하기 위해 X-ray diffraction(XRD) 및 scanning electron microscope(SEM)을 사용하여 상온에서 성막된 AZO 박막의 특성을 관찰 하였다. 또한 AZO 박막의 PET 기판과의 접합성 및 구부림 시의 안정성을 평가하기 위해 bending test를 진행 하였다. 최적화된 AZO 박막으로부터 기판에 성막 중 열처리공정이나 후 열처리 공정의 진행 없이 35 ohm/square의 낮은 면저항과 약 80 % 이상의 투과율을 얻을 수 있었다. LFTS 시스템을 이용하여 낮은 공정온도에서 AZO 박막을 성막 하였음에도 불구하고 낮은 저항과 높은 투과도 특성을 나타내고 있어 기존의 투명 박막을 대체 할 수 있는 가능성을 제시하였다

• Structural Monitoring and Maintenance
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• v.10 no.4
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• pp.299-314
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• 2023

Long-gauge carbon fiber line (CFL) sensors have received considerable attention in the past decade. However, there is still a need for an in-depth investigation of their measuring accuracy. This study investigates the accuracy of carbon fiber line sensors to monitor and differentiate the flexural behavior of two beams, one reinforced with steel bars alone and the other reinforced with steel and basalt fiber-reinforced polymer bars. A distributed set of long-gauge carbon fiber line, Fiber Bragg Grating (FBG), and traditional strain gauge sensors was mounted on the tensile concrete surface of the studied beams to compare the results and assess the accuracies of the proposed sensors. The test beams were loaded monotonically under four-point bending loading until failure. Results indicated the importance of using long-gauge sensors in providing useful, accurate, and reliable information regarding global structural behavior, while point sensors are affected by local damage and strain concentrations. Furthermore, long-gauge carbon fiber line sensors demonstrated good agreement with the corresponding Fiber Bragg Grating sensors with acceptable accuracy, thereby exhibiting potential for application in monitoring the health of large-scale structures.

• Journal of Technologic Dentistry
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• v.19 no.1
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• pp.37-42
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• 1997

The interfacial bond strengh and microstructural analysis of pre-heat treated porcelain-fusedmetal(PFM) were investigated using a mechanical three-point bending tester and scanning electron microscope(SEM). Four kinds of heat treated samples were prepared as follows ; A: Heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating ${\to}1850^{\circ}F$, hold 3min under vacuum, B: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$ under vacuum conditon, C: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$, holding 3min in the air, repeat same heat treatment process under vacuum condition, D: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$, holding 1min in the air. The three-point bening test result shows that the interfacial bond strength of specimen B and C were higher than that of A and D. The SEM study indicate that Specimen C shows the highest surface density.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2520-2528
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• 2000

Mechanical and physical properties of composite materials make a great difference due to their cure process condition. In order to clarify the effect of cure process condition on the microscopic damage behavior and failure mechanism of Carbon/Epoxy composites, three point bend test has been performed. For this purpose, two kinds of specimens with single adhesive and multiple adhesive layers were prepared. For single adhesive layer, four different types of specimen were used, that is, non-sanding, sanding, cocured, laminated specimens. Three different types of specimen were also used for the multiple adhesive layer, non-sanding, sanding, cocured specimens. Acoustic emission technique has also been employed to monitor the damage progresses associated with each micro-failure mechanism. The characteristics of AE parameters associated with micro-failure mechanism of each specimen were discussed.

• Journal of the Korean Society of Safety
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• v.38 no.2
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• pp.36-43
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• 2023

In this study, a four-point bending test was conducted to assess and detect the damage to reinforced concrete structures using the acoustic emission (AE) technique. Based on the crack investigation results, flexural failure was classified into four stages and compared with the characteristic analysis results of AE parameters. The parametric characterization indicated that the activity of the primary AE signal was high in the early stage, and that of the second signal increased after the flexural cracks stabilized. Because the secondary AE signal included noise generated by friction, parameter-based analysis for damage assessment was performed using the primary signal; the secondary signal was used as complement. The activity analyses of the primary and secondary signals effectively classified crack propagation; however, determining the macrocracks and yielding of reinforcing bars had certain limitations. Nevertheless, applying the damage index with cumulative AE energy is a complementary technique for detecting and assessing structure damage that well detects the occurrence of macrocracks.

• Steel and Composite Structures
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• v.13 no.2
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• pp.123-137
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• 2012

Steel plate-masonry composite structure is a newly-developed type of structural technique applicable to existing masonry buildings by which the load-bearing walls can be removed for large spaces. This kind of structure has been used in practice for its several advantages, but experimental investigation on its elements is nearly unavailable in existing literature. This paper presents an experimental study on the flexural behaviour of four steel plate-masonry composite beams loaded by four-point bending. Test results indicate that failure of the tested beams always starts from the local buckling of steel plate, and that the tested beams can satisfy the requirement of service limit state. In addition, the assumption of plane section is still remained for steel plate prior to local buckling or steel yielding. By comparative analyses, it was also verified that the working performance of the beam is influenced by the cross-section of steel plate, which can be efficiently enhanced by epoxy adhesive rather than cement mortar or nothing at all. Besides, it was also found that the contribution of the encased masonry to the flexural capacity of the composite beam cannot be ignored when the beam is injected with epoxy adhesive.

• Structural Engineering and Mechanics
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• v.75 no.5
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• pp.595-605
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• 2020

In this study, the flexural behaviors of full-scale prestressed concrete box girders are experimentally investigated. Four girders were fabricated using two types of concrete (compressive strengths: 50 MPa and 70 MPa) and tested under four-point bending until failure. The measured parameters included the deflection, the stress and strain in concrete and steel bars, and cracks in concrete. The measurement results were used to analyze the failure mode, load-bearing capacity, and deformability of each girder. A finite element model is established to simulate the flexural behaviors of the girders. The results show that the use of high-performance concrete and reasonable combination of prestressed tendons could improve the mechanical performance of the box girders, in terms of the crack resistance, load-carrying capacity, stress distribution, and ductility.